(1) Field of the Invention
The present invention relates to a single crystal diamond particle having 20.about.60 U.S. mesh (hereafter "mesh" means U.S. mesh) and the method of making the diamond particle. The diamond particle is used as an abrasive for sawing, especially to cut stone, concrete, and asphalt.
(2) Description of the Prior Art
Because stone, concrete, and asphalt are hard and brittle materials, diamond particles, which are used as an abrasive for sawing to cut the above materials, must be of high-strength and not friable. There is a strong mutual relationship between cutting performance (tool life) and particle strength. Moreover, it is well known that the particle strength depends on the perfection and symmetry of the diamond particle shape.
When there is a lack portion 29 (e.g., a broken portion or a portion not completely grown) at the surface of a diamond particle 28, as shown in FIG. 11A, the strength of the particle decreases depending on the extent of the lack portion. FIG. 11B shows a long and narrow diamond particle 30 and a sharp-edged diamond particle 30. Such diamond particles have low strength due to lack of symmetry. A high-strength diamond particle is required to have no or minimal lack portion and good symmetry.
The environment for growing diamond can cause a lack portion or poor symmetry of the grown diamond product. When growing diamonds have insufficient distance around them, the growing diamonds contact each other or are unnaturally restricted, even though not contacting, by supply of raw material and the surroundings. For these reasons, many synthesized diamond particles have lack portion(s) and bad symmetry. Therefore, it is necessary to have sufficient distance between growing diamonds to synthesize high-strength diamonds.
However, providing sufficient distance is contrary to economical demands, which require manufacturers to grow as many diamond particles as possible in a limited-space diamond synthesizing vessel. It is required industrially to grow diamonds as densely together as possible, maintaining the lowest necessary distance between the grown particles.
There are generally two methods of synthesizing a diamond particle, which methods are described below.
The first method, as shown in FIG. 12A, is that a compact ("compact" is defined as a powder or particle compacted in a die or mold), including a mixture of non-diamond carbon powder raw material (usually graphite and hereafter referred to as "raw carbon") and solvent metal powder (usually a combination of Fe, Co, Ni, Cr, and Mn and hereafter referred to as "solvent metal"), for diamond synthesizing is maintained at a thermodynamically stable region for diamond and above the melting point temperature of metal-graphite (usually 5.about.6 GPa and 1300.about.1600.degree. C.). (This method is hereafter referred to as the "powder method.")
The second method, as shown in FIG. 12B, is that a multilayer arrangement of raw carbon plates 7 and solvent metal plates 6 is maintained at a thermodynamically stable region for diamond and over the melting point temperature of metal-graphite, the same as in the powder method. (This method is hereafter referred to as the "multilayer method.")
Comparing these two methods, it is thought that the powder method is superior to the multilayer method in terms of yield since the three-dimensional space of the synthesizing vessel is effectively used, and the multilayer method is superior to the powder method in terms of strength of the resulting diamond particles since interference between synthesized diamond particles is limited in one plane.
For effective manufacturing of intended particle size diamond in these two methods, fine single-crystal diamond particles are dispersed as seed crystals in the mixture or in the solvent metal plate. In this case, diamond particles are synthesized around the seed crystals.
In these manufacturing procedures, the diamond particles are synthesized to larger than the intended particle size, and moreover, many produced diamond particles have lack portions and poor symmetry because of interference at the densely arranged portion.
The multilayer method is proposed and practically used in that the seed crystals 1 are arranged regularly in the solvent metal plate 6 as shown in FIG. 13 to resolve the issue (see, for example, Tokko-shou 63-57099, corresponding to U.S. Pat. No. 4,547,257, and Tokkai-hei 5-23574, corresponding to U.S. Pat No. 5,194,070). This method results in a higher-strength product and a higher yield ratio of the intended diamond particle size than previous techniques. The seed crystals are arranged ideally in a plane, but the yield is insufficient since there is un-used space in the vertical direction.
The seed crystals are isolated by only the liquid phase of the solvent metal under the synthesizing conditions of the diamond, and therefore, the arrangement sometimes results in rough and dense portions of diamonds because of movement of the seed crystals.